The present invention relates to an integrated control, active matrix display means comprising two groups of row electrodes and two groups of column electrodes per image point and the control process for the same.
The invention applies to the field of optoelectronics and mainly to the control of liquid crystal cells, used, more particularly as converters of electrical information into optical information, in the real time processing of optical images and for analogue display purposes.
More specifically, the invention relates to an integrated control, active matrix display comprising in per se known manner a display cell having two facing insulating walls, between which is placed a material having an optical property, such as opacity, a refractive index, transparency, absorption, diffusion, diffraction, convergence, etc. This material can be solid, liquid, amorphous or crystalline.
FIG. 1 diagrammatically shows a known active matrix display cell. FIG. 1 shows two insulating walls, namely a first wall 1 and a second wall 3, whereof at least one is transparent and which are facing one another, being maintained spaced and sealed by a joint 5. A layer of a material 7 having an optical property is placed between these walls.
Over the inner face of the second wall 3 is distributed a first group of n parallel row conductors L.sub.i and a second group of m parallel column conductors K.sub.j, i and j being integers such that 1.ltoreq.i.ltoreq.n and 1.ltoreq.j.ltoreq.m, the row conductors and column conductors crossing one another. Not shown display means outside the display cell make it possible to transmit signals appropriate for exciting material 7 to the row conductors and column conductors.
The term inner faces of wall 1 or wall 3 are understood to be the facing faces of said walls. At the intersection 11 of each row conductor L.sub.i and each column conductor K.sub.j there is a switch R.sub.ij, such as a thin film transistor, connected to a conductor block E.sub.ij.
Thus, with each image point I'.sub.ij corresponds a transistor R.sub.ij connected to a row conductor L.sub.i by the gate, to a column conductor K.sub.j by the source and to the corresponding conductor block E.sub.ij by the drain.
The conductor blocks E.sub.ij are made from a generally transparent conductive material, e.g. indium oxide, while the transistors are e.g. made from hydrogenated amorphous silicon.
The inner face of the first wall 1 is covered with a generally transparent conductive material serving as an opposite electrode 13.
Thus, an image point I'.sub.ij is defined by the overlap region of a conductor block E.sub.ij and the opposite electrode 13, the conductor block E.sub.ij and the opposite electrode forming the coatings of a capacitor between which is inserted a material layer 7.
In the particular case of the liquid crystal taken as an example throughout the remainder of the present text for clarity reasons, the excitation is of the electrical type. The opposite electrode 13 is raised to a given potential, whose value is periodically inverted to avoid deterioration of the liquid crystal. The row conductors and column conductors carry alternating voltages.
In order to select a particular image point I'.sub.ij, an electric signal is supplied to row conductor L.sub.i and this selects the conductive or on state of the group of transistors connected to said row conductor and, in particular, the conductive or on state of transistor R.sub.ij. When transistor R.sub.ij is in the on state, it transmits the electric signal from column K.sub.j to the corresponding conductor block E.sub.ij. Thus, between block E.sub.ij and opposite electrode 13 there appears an electric field which will bring about a collective orientation of the molecules, particularly the liquid crystal between the coatings of the capacitor formed by conductor block E.sub.ij and opposite electrode 13. This collective orientation will modify the optical property of material 7.
By using the selective orientation of the molecules and the punctiform excitation of the liquid crystal, an image will be made to appear on the complete cell while defining same point by point.
In such display means, as a result of the intersections 11 of the row conductors L.sub.i and the column conductors K.sub.j on the inner face of wall 3, short-circuits occur between the row conductors and the column conductors, so that a complete row conductor and a complete column conductor is rendered inoperative during each short-circuit. In the same way, when a transistor R.sub.ij is short-circuited, it renders inoperative the complete row conductor and the complete column conductor to which it is connected.
Visually, isolated defective image points are accepted, but never a group of aligned defective image points corresponding to a complete row conductor or a complete column conductor.
No. FR-A-2 553 218 describes an active matrix display obviating intersections of row conductors and column conductors on the inner face of a wall of the display means. For this purpose, the opposite electrode of the first wall of the aforementioned means is replaced by parallel column conductors with which are associated conductor blocks arranged in matrix-like manner. Moreover, on the inner face of the second wall is also arranged a matrix of conductor blocks facing the first matrix, said conductor blocks being connected to row conductors by switches, such as transistors. Thus, an image point is defined by the overlap zone of two facing conductor blocks.
Such display means make it possible to obviate short-circuits between a row conductor and a column conductor, but a short-circuited transistor can still render inoperative a complete row conductor and therefore a row of image points.